LIFE D CH-2

Chapter 2: Heredity, Prenatal Development, and Birth

Overview

• This chapter examines the role of heredity in development, genetic disorders, prenatal development, teratogens, parental influences, and the birthing process.

Heredity

Nature and Genes

• Nature: Refers to genetics' contribution to development.

• Genes: Specific sequences of nucleotides that serve as recipes for making proteins, located on chromosomes (46 chromosomes in normal human cells, 23 pairs).

• There are approximately 20,500 genes in the human genome (Human Genome Project, 2015).

• Mitosis: Process of cell division creating two identical cells.

• Meiosis: Process of forming gametes (sperm and ova) resulting in cells with half the chromosomes (23).

Genetic Terms

• Genotypes: The sum total of all genes inherited.

• Phenotypes: The expressed physical traits of an individual.

• Homozygous: Same version of a gene from each parent.

• Heterozygous: Different versions of a gene from each parent.

• Dominant and Recessive Genes: Dominant genes mask the expression of recessive ones. Examples of traits include facial dimples (dominant) and red hair (recessive).

• Polygenic Inheritance: Characteristics influenced by multiple genes.

• Incomplete Dominance: Situation where the dominant gene doesn’t completely mask the recessive gene, as seen in sickle cell disease.

Genetic Disorders

• Dominant Disorders: Examples include Tourette’s Syndrome (minor tics) and Huntington’s Disease (fatal, appears in midlife).

• Recessive Disorders: More commonly life-threatening (e.g., cystic fibrosis, sickle-cell anemia).

• Sex-linked Disorders: Affects the X chromosome (e.g., hemophilia, color-blindness). Males are disproportionately affected due to having only one X chromosome.

Chromosomal Abnormalities

• Defined as inheriting too many or too few chromosomes. Common cause is advanced maternal age.

• Down Syndrome (Trisomy 21): Characterized by three 21st chromosomes leading to intellectual disability and distinct physical features.

• Turner Syndrome: Affects females with an X chromosome missing (XO).

• Klinefelter Syndrome: Affects males with an extra X chromosome (XXY).

Prenatal Development

Overview of Periods

1. Germinal Period: Conception to implantation (~14 days). Formation of zygote and later a blastocyst.

2. Embryonic Period: Begins at implantation; major organs and structures develop. Most vulnerable to teratogens.

3. Fetal Period: From 9 weeks to birth; maturation of organs and systems, characterized by significant growth and brain development.

Prenatal Brain Development

• Begins in the third gestational week as stem cells differentiate and form neural structures. Growth continues until mid-gestation.

• Neurogenesis: Formation of neurons completed by five months, with neural migration and dendrite/axon development continuing postnatally.

Teratogens

• Environmental factors that can cause birth defects (e.g., alcohol, tobacco, pollutants).

• Factors affecting teratogen impact include timing, amount, number of teratogens, genetics, and infant sex.

• Alcohol: Leading preventable cause of intellectual disabilities (FASD spectrum).

• Tobacco: Linked to low birth weight and respiratory issues.

• Illicit drugs: Associated with preterm birth, addiction, and developmental issues.

Maternal and Paternal Factors Affecting Prenatal Development

• Age: Older mothers (over 35) at higher risk for complications, but may also offer stability.

• Teenage Mothers: More risk for complications and low birth weight.

• Gestational Diabetes: Occurs in about 7% of pregnancies; untreated can lead to serious outcomes.

• High Blood Pressure: Affects about 8% of pregnant women.

• Rh Disease: Occurs when the mother's blood lacks the Rh factor, which can affect future pregnancies.

Prenatal Assessment

• Assessments include blood tests, ultrasounds to check fetal development, and procedures like amniocentesis for genetic conditions.

Birth Process

Preparation

• Expectant parents should prepare physically and mentally for childbirth, learning about their roles.

Stages of Vaginal Delivery

1. First Stage: Dilation of the cervix.

2. Second Stage: Delivery of the baby.

3. Third Stage: Delivery of the placenta.

C-Sections and Induced Birth

• C-sections are often necessitated by complications, while labor may be induced for health concerns.

Assessing the Neonate

• Apgar Score: Assesses the newborn's condition soon after birth based on heart rate, respiration, muscle tone, reflex, and color.

• Problems in Newborns: Low birth weight, preterm birth, and anoxia can lead to long-term developmental issues.